The principal goal of this project is to utilize dispersed parathyroid cells to study the regulation of parathyroid hormone (PTH) secretion from normal and abnormal parathyroid tissue. The role of cyclic nucleotides in PTH release from dispersed bovine parathyroid cells will be determined by evaluating the effects of divalent cations and diverse secretagogues on adenylate cyclase, phosphodiesterase, and protein kinase activities. Abnormalities in calcium- and secretagogue-stimulated secretion will be assessed in pathologic parathyroid tissue. Possible malregulation of the intracellular content and action of mediators such as cyclic AMP will be studied in terms of alterations in the control of these functions in normal parathyroid cells.